This invention refers to a bandwidth optimiser, dynamically operating in connections to multi-bearer systems for radio communications, especially useful in the so-called DECT systems for the transfer of data packets for short distances. The bandwidth optimizer according to the invention does not concern, however, only said implementation. It can be in fact useful also in UMTS systems.
More particularly, the bandwidth optimiser according to the invention is applicable in the field of the radio access. It can be applied to each fixed system that provides the transmission of packets using Digital Enhanced Cordless. Telecommunications (DECT) technology with data service profiles allowing multi-bearer connections (e.g. B1 and subsequent)
As it is well-known, DECTxe2x80x94standardised according to ETSI rules ETS 300 175 (1-9), second edition 1996xe2x80x94is based on a micro and pico-cellular radio communication system that provides low-power radio (cordless) access between portable parts (PPs) and fixed parts (FPs) at ranges of few kilometres, allowing transmission of voice and data. Thus the DECT radio access network is a radio based access network, enabling connection of subscribers without conventional wiring between local exchange and subscriber""s house. It is suitable both for urban and suburban areas with densities of 10 to 50,000 subscribers per km2.
It is advisable to consider the present state of art in the field of the present invention.
Consider that DECT uses a multi-channel, time-division multiple access, time-division duplex (MC-TDMA/TDD) radio interface and operates in the range 1.88-1.9 GHz. The radio bandwidth is split into ten channels in the frequency domain. Each of these ten channels is divided, in turn, in the time domain into a cycle of 2xc3x9712 repeating (duplex) time slots. The time slots may have either a protected format, through the Cyclic Redundancy Codes (CRCs) or not.
The first application of DECT regarded only voice transmission, but DECT has proven a very flexible system which can find other uses: particularly it includes the so-called Data Service Profiles (DSPs) that make it suitable to all current applications of data transmission, such as colour fax, e-mail, file transfer, group xc2xe fax, real-time video, video messaging and so on.
Nowadays, the greatest interest is towards the Internet access both for data transmission and for applications such as voice over IP and Home Working for the remote access to a corporate Intranet.
These applications require strong constraints on the quality of transmission, so that a DECT system necessitates sending data with a low error percentage (the optimum obviously being 0). For this purpose the need to have a protected format for the time slots, retransmissions or, in the most delay sensitive cases, Forward Error Correction (FEC) is stronger in data than in voice transmission, obviously to the detriment of the introduced delay that in turn effects the performance of the system (for instance in terms of effects on TCP/IP).
Thus, in the current implementations utilising DECT, the error correction service on the Medium Access Control (MAC) of the DECT protocol stack is implemented so as to allow the time slots to have a protected structure, which is guaranteed by the CRCs, a mechanism to detect errors. Every time an error is detected the whole slot is retransmitted.
A structured analysis that provides estimation about the error probability of slot and Service Data Units (SDUs) with respect to the bit error rate, independent of application in order to evaluate the performances of a DECT system in terms of delay, is missing in the literature and in the state of the art. Only some evaluations about the voice service can be found, but in this case the overall number of test bits is for example 84, in particular 84 bit per full slot of 420 bits.
The inventors calculated the error probability of the time slot and of the related SDUs with or without retransmission and showed how these probabilities change with respect to the bit error rate. Furthermore, they carried out an analysis of the probability for a certain number of retransmissions and the delay to occur, as a function also of the number of bearers (carrier/time-slot combinations) used in the connection.
This strategy of analysis developed in the above mentioned frameworkxe2x80x94which is absolutely new for such a framework, also for the mathematical approach employedxe2x80x94has importance not only because it is applicable for systems that use a DECT profile with protected format for the time slots, with or without retransmissions, independently of the application, but also because it allows to deploy the system in the best way according to the quality of the air interface. In fact, it is possible to assign to each connection a suitable value for the bandwidth with respect to bit error rate. So, a system of bandwidth optimisation has been designed, which has bit error rate as input and takes into account the traffic load. Such a system is absolutely new, since it was never used and no trace is found in the literature.
Starting from the analysis above, this invention more specifically refers to a bandwidth optimiser, dynamically operating in connections in radio communications to multi-bearer systems, especially useful in DECT systems for the short-distance transfer of data packets and it is characterised in that comprises: a first block, to which bit error rate is fed and which calculates the most likely number of re-transmissions required by the quality of air interface; a second block which receives from the first one said number of retransmissions and provides, on the basis of such a number, a table giving the change in transmission time with in the number of bearers; and a third block, which is fed by the second one and decides the optimal number of bearers to be allocated to the connection and the output of which feeds a device (RA) for resources allocation, said optimal number of bearers representing the maximum band to be allocated to the connection, depending also on the traffic intensity.
In this optimiser, the first block considerates bit error rate (BER) during each connection as a constant, which is calculated during the previous connection and calculates the most likely number of retransmissions, which are necessary for a correct transmission as sum of the probability of error in N time slots upon changes in the bit error rate, while the second block calculates time to transmit a unit of service data, plus delay due to the retransmissions, also connected with the number of bearers, and the third block determines the optimal number of bearers to be. allocated, taking into account traffic intensity, thus delays, as well as the quality of interface air.